This invention relates generally to marking integrated circuit packages and more particularly to indelibly marking metal packages for integrated circuits.
In the electronics industry, components are often sealed in standard sized packages. Diverse components, therefore, look the same and some marking must be included on the package to differentiate them.
Various kinds of ink have been used to mark packages. The ink is readable when applied, but wears off over time. When exposed to severe environmental conditions, the ink wears off faster. For packages made of metal or other material to which ink does not readily adhere, the markings wear off very rapidly. Worn off markings are a particular problem in military applications. Military procurement standards require that electronic components incorporated in military systems have readable markings even after exposure to severe environmental conditions. Since many components for military use are enclosed in metal packages, ink marking is inadequate for military applications.
Laser marking has also been contemplated. Laser marking apparatus have been developed and are sold commercially. In these apparatus, the package to be marked is mounted in the path of a laser beam. The marking apparatus contains optical elements which can direct the beam to various points on a surface of the package. By appropriate control of these optical elements, often by a computer running a software program, the laser beam traces out the desired markings on the package.
Various parameters of the apparatus might be controllable to affect the appearance of the marking. In a commercially available apparatus, the controllable parameters might include: the width of lines traced out by the laser beam; the speed at which the laser beam traces out a line; the Q-switch frequency of the laser; the diameter of the aperture through which the laser beam passes; and the current supplied to the laser.
The energy in the laser beam "burns" or "blasts" away parts of the package to cut grooves in it. A problem with laser marking is that the visible contrast between the grooves and the rest of the package can be very slight. Thus, even though the grooves are indelible, the markings can not be easily read. An additional problem with laser marking of metal is that the laser, being a light beam, tends to reflect from metal surfaces. If too much of the beam reflects from the surface, no mark can be made.
To solve these problems, a four pass marking process has been suggested. In other words, for each line to appear on the package, the laser beam passes over the same spot four times with different combinations of the parameters for aperture size, Q-switching frequency, speed and line width. The value of the current parameter is set empirically to a value which makes readable marks.
It has been observed with the parameters listed in Table I, the current could be adjusted to produce readable lines. The parameters are used with an Nd:YAG laser producing a 0.0059 inch wide beam at a wavelength of 1.064 nanometers and having a focal length of 2.88 inches. The lines produced are not simply grooves, but turn dark during the marking process.
TABLE I ______________________________________ PASS 1 2 3 4 ______________________________________ Aperture OUT IN IN OUT Q-Switch Frequency (KHz) 6 3 10 CW Line Sweep (min/sec) 200 400 4 80 Line Width (mm) N/A N/A 4 N/A ______________________________________
The entry "IN" in Table I indicates an aperture of approximately 80 mm is placed in the path of the laser beam. The entry "OUT" indicates the aperture is taken out of the path of the laser beam.
The entry "CW" in Table I for Q-switch frequency stands for continuous wave. In other words, the laser produces an output continuously as opposed to a pulsed output. The entries "N/A" for line width values implies that the line width is roughly as thick as the laser beam. In contrast, where a numerical value is given for the line width parameter, it implies the laser beam is oscillated perpendicular to the direction of the line with the amplitude of the oscillations given by the value for line width.
A problem with marking packages according to this technique is that it is inconvenient to empirically adjust the current to get readable markings. Several packages might be ruined in the process of adjusting the current, which can involve a significant cost, especially if gold plated packages are used. Additionally, in production facilities where packages are marked continuously, the current may need to be adjusted periodically due to changes in laser operation or the operation of the marking apparatus. The time and cost of empirically adjusting the current periodically is undesirable. Alternatively, supervision of the marking process to ensure the marking is adequate is also undesirable.
An additional problem with the known marking process is that the current may need to be adjusted for each package to be marked. Military procurement specifications require electronics components to be enclosed in packages comprising a base layer of Kovar, a plating of nickel, roughly 100 to 300 microinches thick and a plating of gold roughly 50 to 150 microinches thick. This specification allows considerable variations in the thicknesses of the plating layers and the known process does not always produce uniform dark markings for all thicknesses allowed by the specification.
It would be desirable to simply and inexpensively set the parameters of the laser marking apparatus to produce readable markings on all packages regardless of variations in the thicknesses of the layers in the package.